Radio Frequency Identification (RFID) systems are becoming more and more popular for monitoring and tracking objects, animals, and sometimes even people. For example, RFID systems are used in stores for monitoring and tracking items for sale, in libraries for tracking books, in warehouses for tracking goods, on farms for monitoring cattle or livestock herds, and in roadway tolling systems for tracking passing vehicles. As the costs of manufacturing RFID components continue to decrease and the technology associated with RFID components improves, people are finding more and more applications in which to employ RFID technologies. Additionally, people are continually improving the technology and finding ways to circumvent performance limitations associated with RFID systems.
RFID systems typically consist of radio frequency (RF) tags, RF tag readers, and some type of computer running software to process information obtained from tag reads, or interrogations. The tags typically respond to an RF query, or interrogation, signal broadcast initiated by the tag reader. The tags usually send out preconfigured information, such as serial numbers or other data stored within differing types of memory devices coupled to the tags. RFID tags and tag readers usually operate without any line-of-sight requirements. The tags and readers can usually also receive and transmit signals through nonconductive materials.
Even though RFID systems have many benefits, the systems also have numerous inherent problems. First, tag readers generally have difficulties focusing RF transmissions to limited or confined areas where the tags are located. In other words, the interrogation signals are generally dispersed, or transmitted, beyond the desired sample areas. Consequently, tags located outside of the desired sample areas may detect the interrogations signals from the readers and respond by sending back their particular information. Implicit in this problem is the fact that tags, similar to readers, cannot generally focus or limit their broadcasts to a particular reader. Accordingly, as RFID systems grow in complexity, involving large numbers of tags and readers, this problem of crosstalk can introduce problems that need to be addressed.
Another problem encountered in using RFID systems is that of false reads. False reads generally arise due to the low-cost and low-power constraints of RFID tags. False reads can be further divided into two different types, false negative reads and false positive reads. False negative reads usually refer to situations where RFID tags are present in the sample area but which are not read during an interrogation, leading to the mistaken belief that objects associated with the tags are not present. Similarly, as alluded to above, false positive reads describe situations where RFID tags might be read even though they are located outside desired sample areas. This fools RFID readers to mistakenly conclude that objects attached to tags are present in the sample area, when in fact they are not.
For example, one application employing an RFID system may be a manufacturing facility having an assembly line for the manufactured products, wherein RFID tags are used to monitor and track the products on the assembly line. On assembly lines, containers are often placed next to each other. The close proximities of tags on the lines can cause readers for particular containers to pick up false positives from tags within neighboring containers when, for example, the readers attempt to take inventories of the particular containers.
Solutions to date have many drawbacks. One solution provides a “smart” container having dedicated tag readers on individual steel containers. This approach may help reduce the existence of sensing false positives, as the steel containers help focus the signal transmissions for the individual readers. However, this approach does not attempt to discern whether any of the tag reads are genuine or false. Another solution utilizes two readers, an entry reader and an exit reader, for individual containers on an assembly line. While this method may help reduce false positive reads, it unfortunately does not provide for any container inventory tracking or container integrity monitoring. In other words, this solution does nothing to address items being added to or removed from the containers between the time of the entry reader scan and the exit reader scan. What are needed, therefore, are methods and systems to detect the presence of new tags and associated objects for individual containers, or sample areas, to help determine if they are genuine or false tag reads, and to monitor or track container inventories.